1. Field of the Invention
The present invention relates to a disc and hub assembly for an electromagnetic clutch of a compressor, and more particularly to a disc and hub assembly for an electromagnetic clutch of a compressor wherein a bumper is interposed between its disc and plate spring to reduce noise and impact during on/off of the clutch, and is prevented from separating due to centrifugal force or being damaged, e.g., being torn off, thereby improving durability and further improving noise reduction effect.
2. Background of the Related Art
A compressor is a component of an air-conditioning system of an automobile. Power is selectively transmitted from an engine to the compressor via a pulley by means of interruption of an electromagnetic clutch. The compressor then compresses a refrigerant, which is supplied from an evaporator, and sends it to a condenser.
The electromagnetic clutch, which transmits the power from the engine to the compressor, comprises: a pulley rotatably installed on the compressor via a bearing; a field core unit supported on the compressor in such a manner that it is inserted into the pulley and adapted to generate an electromagnetic force in accordance with application of electric power; and a disc and hub assembly connected to a driving shaft of the compressor via a hub and configured in such a manner that its disc is attracted to or separated from a friction surface of the pulley by means of the electromagnetic force, which is generated by an electromagnetic coil of the field core unit, to selectively transmit the power from the engine to the driving shaft of the compressor.
FIGS. 1 and 2 show an example of the disc and hub assembly, which uses a number of leaf springs, among the configuration of the above-mentioned electromagnetic clutch. As shown in the drawings, the assembly includes a hub 10, a disc 20, and leaf springs 30.
The hub 10 is composed of a hub body 11, which is provided with a coupling hole 11a having a spline (not shown) formed therein for spline coupling with a driving shaft (not shown) of a compressor, and a flange 12 formed around an outer peripheral surface of the hub body 11 near an end of the body 11.
The flange 12 of the hub 10 has a number of (e.g., three as in the drawing) rivet coupling holes 12a formed thereon.
The disc 20 has a through-hole 22a formed in its center, the diameter of which is larger than that of the flange 12 of the hub 10.
More specifically, the disc 20 comprises an outer ring 21; an inner ring 22 positioned inside the outer ring 21 in such a manner as to be spaced apart from the outer ring 21 and the flange 12 of the hub 10 by a regular interval; and bridge portions 23 which connect the outer ring 21 with the inner ring 22 and define arc-shaped slots 24 together with the outer and inner rings along its circumferential direction.
The outer ring 21 has a number of (three in the drawing) rivet coupling holes 25 formed therein.
The flange 12 of the hub 10 is inserted into the through-hole 22a of the disc 20 to be located in position in the through-hole 22a. 
The leaf springs 30 are bent with a predetermined angle, and have holes 31a, 33a, and 32a formed at both ends 31 and 33 and bent portions 32 thereof.
One ends 31 of the leaf springs 30 are coupled to the outer ring 21 in such a manner that rivets 55 pass through the rivet coupling holes 25 of the outer ring 21 and the holes 31a of the leaf springs 30 which are matched with each other.
Dampers 40 of rubber material are fit into the holes 33a, which are formed on the other ends 33 of the leaf spring 30. Then, the dampers 40 contact and support the inner ring 22, so that the other ends 33 of the leaf springs 30 are spaced apart from the inner ring 22 by a predetermined distance.
The holes 32a, which are formed on the bent portions 32 of the leaf springs 30, are coupled to the rivet coupling holes 12a, which are formed on the flange 12 of the hub 10, via rivets 50.
The conventional disc and hub assembly 1, configured as above, is operated as follows: when electric power is applied to an electromagnetic coil of its field core unit (not shown), the electromagnetic coil generates an electromagnetic force and power from the engine is transmitted to the disc 20, at which time the disc 20 is then moved toward a rotating pulley (not shown) and is attracted to the friction surface of the pulley. As such, a friction force makes it possible to transmit the power from the engine to the driving shaft of the compressor via the disc 20 and the hub 10.
When the application of electric power to the electronic coil is interrupted, the disc 20 is separated from the friction surface of the pulley, due to an elastic restoration force of the leaf springs 30, and power is no longer transmitted to the driving shaft of the compressor.
However, the conventional disc and hub assembly 1, as mentioned-above, has a problem in that a severe noise is generated during on/off operation of the electromagnetic clutch, due to a structural defect, and thus it is not applicable to other products.
In particular, when electric power is applied to the electronic coil and the disc 20 is attracted to the friction surface of the pulley, a metallic hitting sound is generated due to a collision between the disc 20 and the pulley to generate a noise. Such a noise may be transmitted to and annoy a driver in the passenger's room.
In addition, since the arc-shaped slots 24 of the disc 20 are exposed to the outside, dust or alien substances may be introduced into the assembly through the slots 24 and reach the friction surface of the pulley. Then, the friction force between the pulley and the disc 20 is decreased, and hence the power transmission efficiency is deteriorated. The disc 20 or the friction surface of the pulley may also be damaged.
Furthermore, the durability of the leaf springs 30 is problematic.